1. Field of the Invention
The invention relates to a magnetic resonance spectroscopy method where a plurality of sequences act on an examination zone in the presence of a uniform, steady magnetic field, each sequence comprising at least three RF pulses, the distance between the first two RF pulses being equal to the reciprocal value of twice the scalar coupling constant J, between and after the pulses there being applied magnetic gradient fields having an amplitude and a duration so that spin resonance signals occurring after the third RF pulse are determined exclusively by double quantum coherence.
2. Description of the Related Art
A method of this kind is described by D. M. Freeman et al, SMRM Abstracts (San Francisco), 212 (1988) and by A. Bax et al, Chem. Phys. Lett., Vol. 69, No. 3, pp. 567-570 (1980). According to the known method, a magnetic gradient field is switched on and off before and after the last RF pulse. The time integral over this field after the last pulse exactly equals twice the corresponding integral before this pulse. It is thus achieved that only double quantum coherences influence the spin resonance signal. Single quantum coherences, notably the signals originating from water-bound protons, are then strongly suppressed.
In the publication by Freeman et al this method is used to determine the concentration of lactate independently of the concentration of fat or lipids. The Larmor frequencies of protons bound to fat and to lactate are very close to one another. In order to enable separation of these two components, a two-dimensional frequency spectrum is generated according to the known method. To this end, the so-called evolution time between the second and the third RF pulse is changed in steps, the spin resonance signals thus obtained being subjected to a two-dimensional Fourier transformation in order to obtain a two-dimensional frequency spectrum in which fat and lactate can be suitably separated from one another.
Two-dimensional frequency spectra require very long overall measuring periods and are susceptible to movements in the examination zone. Therefore, it would be useful to be able to determine the lactate concentration in a one-dimensional frequency spectrum independently of the fat concentration. This is hampered by the fact that one frequency component of lactate-bound protons is situated in the direct vicinity of the Larmor frequency of water-bound protons and that the other frequency component of lactate directly neighbours a fat component which is also present in the double quantum spectrum.